How do you rewrite the exponential expression as a radical expression #b^(- 4/7)#?
There are two laws of indices involved. A negative index indicates a fraction (the reciprocal with a positive index) and a fractional index means there is a power and a root.
Let's deal with the negative in the index first. This simply means that the base is in the denominator and the index is positive:
The numerator of a fractional index is a power,
the denominator of a fractional index is a root.
This gives us